1. Field of the Invention
The present invention relates to a plasma processing method, wherein the inner wall of a treatment container, the surface of a susceptor, the surface of a substrate, and the like, can be cleaned in a short time period, thereby to form a high-quality thin film.
2. Description of the Related Art
A CVD (chemical vapor deposition) method is widely known as a conventional method of forming a thin film on a substrate such as a semiconductor wafer. The CVD method is performed, for example, by employing a cold wall CVD apparatus. In the cold wall CVD apparatus, in order to suppress an undesirable deposition, a substrate is heated via a susceptor. FIG. 1 shows an example of the cold wall CVD apparatus. As shown in FIG. 1, the apparatus comprises a cylindrical vacuum container 1 having a stepped portion, and a cylindrical high-frequency electrode 5 connected to a high-frequency power source 6 and inserted into the inside of the vacuum container 1 through an opening formed in the bottom face of the vacuum container 1. A flange is provided on a lower peripheral portion of the high-frequency electrode 5. The flange is attached to the bottom face of the vacuum container 1 via an annular insulating member 8. An upper smaller-diameter portion of the container 1 serves as a gas introducing chamber 1a, and a lower larger-diameter portion of the container 1 serves as a treating chamber 1b. The upper face of the gas introducing chamber 1a is provided with gas introducing pipes 4 for introducing raw material gas into the container 1. The side face of the treating chamber 1b is provided with gas discharging pipes 9 for discharging the raw material gas. A susceptor 3 for mounting a substrate 2 thereon and heating the substrate 2 is arranged within the treating chamber 1b.
With use of the cold wall CVD apparatus shown in FIG. 1, a thin film is formed in the following manner. At first, the pressure within the vacuum container 1 is reduced to a predetermined value. The raw material gas for forming the thin film is introduced into the treating chamber 1b through the gas introducing pipes 4 and gas introducing chamber 1a. Then, the thin film is formed by a normal thermal CVD method. After the thin film is formed, the raw material gas is discharged through the gas discharging pipes 9.
In the above cold wall CVD apparatus, a process of cleaning the surface of the substrate is performed by using a plasma as a pre-treatment, in order to eliminate a spontaneous oxide film or the like from the surface of the substrate such as a semiconductor wafer. It is desirable that the spontaneous oxide film be completely removed from the surface of the substrate, since it acts as an electrical insulation film which is disadvantageous for achieving high-integration of 4 M or 16 M. Also, it is desirable that impurities be eliminated from the inner wall of the treatment container and the surface of the susceptor. There is a fear that such impurities may be adhered to the surface of the substrate, while the thin film is formed on the substrate. The cleaning process may be performed to eliminate impurities not only from the surface of the substrate but also from other parts. In general, the cleaning process is performed as follows. Namely, a chemically stable cleaning gas is introduced into the container 1, in lieu of the material gas. A high-frequency electric current is supplied to the high-frequency electrode 5, so that the gas introduced into the vacuum container 1 is brought into a plasma state. This plasma is used for etching the part to be cleaned, thus completing the cleaning process.
In general, in the above plasma treating apparatus, a large space is provided above the substrate in order to smooth the flow of the material gas, and to increase the ratio of the amount of material gas fed to the container to the amount of material gas consumed in the container. It is thus possible to obtain a uniform thickness and a uniform quality of the thin film. Because of this structure, a distance between the high-frequency electrode and the inner wall of the vacuum container corresponding to a ground electrode becomes large. Thus, when an electric field is generated between the high-frequency electrode and the inner wall of the vacuum container to produce a plasma, the intensity of the generated electric field is decreased. It is, therefore, difficult to obtain a high-energy plasma necessary for performing the etching process. This being the case, the cleaning of the substrate surface and susceptor surface cannot be completely performed, and the time necessary for the cleaning becomes longer. Therefore, the time required for the entire treating process becomes longer.
On the other hand, in the case of the plasma etching and the plasma CVD, a magnetic field is produced together with an electric field, thereby to easily produce a plasma and keep the produced plasma in a stable condition. For example, Japanese Patent Disclosure (Kokai) No. 56-48238 and Japanese Utility Model Publication No. 60-26094 disclose plasma treating apparatus wherein a permanent magnet or an electromagnet is embedded in an electrode. In addition, Japanese Patent Publication No. 59-27212 discloses a plasma reaction apparatus wherein a static magnetic field is applied across two opposite electrodes in parallel to the electrodes. Furthermore, Japanese Patent Disclosure (Kokai) No. 60-156547 discloses a plasma treating method wherein magnetic field is applied in a direction perpendicular to the flow of a plasma, and the plasma is irradiated onto an object in an oblique direction.